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\begin{document}

%-------------------------------------------------------------------


\section*{polyhedron}

\hypertarget{context}{}\subsubsection*{{Context}}\label{context}

\hypertarget{topology}{}\paragraph*{{Topology}}\label{topology}

[[!include topology - contents]]

\hypertarget{contents}{}\section*{{Contents}}\label{contents}

\noindent\hyperlink{idea}{Idea}\dotfill \pageref*{idea} \linebreak
\noindent\hyperlink{polyhedra__polyhedral_spaces}{`Polyhedra = polyhedral spaces'}\dotfill \pageref*{polyhedra__polyhedral_spaces} \linebreak
\noindent\hyperlink{related_concepts}{Related concepts}\dotfill \pageref*{related_concepts} \linebreak
\noindent\hyperlink{references}{References}\dotfill \pageref*{references} \linebreak


\hypertarget{idea}{}\subsection*{{Idea}}\label{idea}

The term \emph{Polyhedron} is used in various senses in [[topology]] and [[geometry]]. Geometrically one has the following:

\begin{defn}
\label{}\hypertarget{}{}
A \textbf{polyhedron} is a 3-[[dimension]]al [[polytope]].

\end{defn}
An alternative use of the term is

\hypertarget{polyhedra__polyhedral_spaces}{}\subsection*{{`Polyhedra = polyhedral spaces'}}\label{polyhedra__polyhedral_spaces}

In classical algebraic topology, (e.g. in Spanier's book), there is another use for the term, more or less as an abbreviation for `polyhedral space'. In this sense, it is given by

\begin{defn}
\label{}\hypertarget{}{}
A space $X$ is called a \textbf{polyhedron} if it is homeomorphic to the [[geometric realisation]] of a [[simplicial complex]] and hence has a [[triangulation]].

\end{defn}
The classical study of polyhedra in this second sense has been one of the sources for methods and applications in algebraic topology, and it is often useful to go back to see the motivations and applications in the older sources. For instance, shape morphisms between polyhedral spaces are just homotopy classes of continuous maps so the Cech invariants of polyhedra coincide with their ordinary `standard' invariants.

\hypertarget{related_concepts}{}\subsection*{{Related concepts}}\label{related_concepts}

\begin{itemize}%
\item [[polygon]]


\item [[scissors congruence]]



\end{itemize}
\hypertarget{references}{}\subsection*{{References}}\label{references}

\begin{itemize}%
\item [[Edwin Spanier]], \emph{Algebraic Topology} , McGraw-Hill, 1966.

\end{itemize}
(The link gives an up-to-date bibtex reference to the more recent edition of this.)

[[!redirects polyhedra]] [[!redirects polyhedral space]]



\end{document}